He was left with cuts to his face and there are fears he might have been so psychologically damaged he will never finish his training as a guide dog.

Terrified puppy Milo is training through the Seeing Dogs Alliance

The black pup is four months into his training with the Seeing Dogs Alliance and his trainer, who did not wish to be named, said he had been doing very well.

As she left the shop with her teenage son and Milo, they walked past the adult terrier - held by a girl aged around eight.

"The next thing I knew this dog had locked its jaw onto the side of Milo's face..." - Milo's trainer

The trainer, who has another dog of her own, said: "I saw the dog and didn't think anything of it. Milo is incredibly well behaved - he just walked past.

"But it was all a bit of a blur, really. The next thing I knew this dog had locked its jaw onto the side of Milo's face.

"It was petrifying, I thought he was going to bite the side of Milo's face off. There was no way the Staff was letting go, and I was so frightened I tried to kick him away, but it didn't make any difference.

"Then I pushed Milo towards him – I knew if the Staff pulled or shook, Milo's face would be completely lacerated.

"Milo was squealing in panic, it was just horrendous."

Six-month-old labrador Milo was attacked in Strood

According to the woman's son, a group of men from the shop ran over to help and eventually got the terrier off Milo.

The dog immediately ran back into the safety of the shop, whimpering and trembling from nose to tail.

The puppy suffered puncture wounds to his face, which are now infected. He is on antibiotics.

It costs around £15,000 to train a guide dog and if Milo has been psychologically damaged by the attack and fears other dogs from now on, it might render him useless as a guide.

The scene of the dog attack outside Tesco in Strood

Geoff Parker, from Seeing Dogs, said: "Obviously we hope that won't happen, and we may not know for a few weeks if it's an issue.

"If it is we will make sure Milo is rehomed as a pet."

Police are investigating reports of a dog "being dangerously out of control in a public place and an assistance dog being injured in a public place".

Inquiries are ongoing.

Rachel Potter was bitten by a Staffordshire bull terrier

It comes a month after another Staffordshire terrier, Chase, was put down because it escaped under a fence and attacked a neighbour sunbathing.

Rachel Potter, of Hawthorn Road, Strood, needed hospital treatment after the two-year-old dog left her with bite marks on her arm.

And in June, Rik Tye had to watch video footage of his cat being ripped apart by three wild dogs on the Medway Gate estate in Strood.